The present invention relates to the fusion of non-woven sheets or webs of fibers to fuse and/or perforate the sheets or webs in preselected areas.
It is known in the prior art to subject non-woven sheets or webs of synthetic fibers to textile needling operations in order to stabilize or consolidate the sheet or web or to bind another sheet or web thereto. While this technique does provide a certain degree of stabilization or strengthening of the sheet or web and/or binding of another sheet or web thereto, it is well accepted that for certain end uses, this treatment is insufficient to produce a finished product and accordingly some form of additional fusing or binding is necessary.
It is also known that thermoplastic, non-woven sheets or webs of fibers may be stabilized or consolidated and/or bonded to another sheet or web, either over its entire surface or in preselected areas, by subjecting the sheet or web to radiant heat or by passing the same over heated rollers, both under pressure and at a temperature sufficient to fuse at least some of the fibers of the sheet or web. However, these methods are somewhat inflexible as to their operating conditions, and, therefore, it has been difficult to operate at commercially economical line speeds and the rolls utilized to heat preselected areas are expensive, time consuming to change and therefore lack versatility. Another major difficulty of such methods lies in the fact that the heating step must be carefully controlled to insure that the fibers are brought to the correct temperature and maintained at that temperature for a proper length of time and under carefully controlled pressure in order to produce the desired end product. Overheating of the sheet or web will result in total fusion of the fibers while underheating will cause insufficient fusion. If the sheet is underheated, it results in a structurally weak material. On the other hand, where the sheet or web is fused over its entire surface, it acquires a harsh hand and is too stiff or paper-like to be useful for a number of purposes.
Yet another method of consolidating or binding a sheet or web of thermoplastic fibers, either over the entire surface thereof or in predetermined areas, has been suggested in which the temperature is maintained well below the fusion temperature of the thermoplastic fiber but at which tack develops. This technique often results in inadequate fusion.
Other techniques which are applied to bind or consolidate in preselected areas or over the entire surface of a sheet or web of synthetic fibers, involve the deposition of polymerizable or copolymerizable materials on the sheet or web and effecting copolymerization or polymerization by exposure to light, the deposition of graft polymers on the sheet or web and effecting polymerization by passing the sheet or web over heated rollers or the deposition of chemically reactive liquids on the sheet or web and effecting chemical reactions by exposure to heat or light. These techniques all have the common disadvantage of requiring somewhat complicated equipment to deposit the treating materials on the sheet or web and also suffer from the inherent disadvantage of requiring additional materials, which are in and of themselves expensive. Further, in addition to the requirement of extra equipment for effecting deposition of the binding material on a sheet or web, such techniques also require means for drying or curing the adhesive or other material. Finally, these methods do little, if anything, to achieve the desired finish on the non-woven fabric and, hence, further steps are required to provide the proper finish. In this instance, the finishing may consist of resaturation and perhaps curing.
Yet another technique for fusing thermoplastic, synthetic fiber materials, particularly as a substitute for sewing in the production of quilted multilayer materials, is the utilization of ultrasonic energy to bond or weld the layers together at preselected points. In this technique, pins are placed in the required pattern across the entire width and around the circumference of a roll. The roll is fitted with a series of sonic "horns", which bear against the pins, and ultrasonic energy is imparted to the pins. This high-speed vibration develops heat in the textile materials at the points of contact with the pins and the pressure exerted by the pins presses the molten mass into weld spots. While this technique effectively accomplishes the desired purposes of producing a quilted material having good flexibility and a soft hand, and excellent binding of the layers is attained, there are obvious disadvantages. Among these are the facts that the equipment is expensive, a great deal of skill is required, both in the operation and maintenance of the equipment, the pattern can be changed only with great difficulty and the equipment is relatively delicate.
It is therefore an object of the present invention to provide an improved method of fusing or perforating a sheet or web of non-woven fibers, containing at least some thermoplastic synthetic fibers, at preselected points or areas, which overcomes the above-mentioned disadvantages of the prior art as well as others not mentioned herein. Another object of the present invention is to provide improved sheet or web materails of non-woven fibers, containing at least some thermoplastic synthetic fibers.